Sciencemadness Discussion Board

LiL help with Solution Extraction

Sigerson - 5-3-2014 at 20:31

Greetings all,
This is my first post outside of the legal and societal forum so before I continue, please forgive me in advance if what I'm asking here is readily available elsewhere. I did search to no avail so that said.....

I'm working through a few labs found in Bob Thompson's illustrated guide to chem. He has been amazingly kind and patient with me as I bombarded him with myriad questions initially but I think it's time to return that favor and give him a break. And so, I turn to you fine folks.

In the lab on solvent extraction, I applied lighter fluid to a test tube filled with iodine solution (1.27% I and 1.67% KI) and water and sure enough, in short time a deep purple layer formed along the top which I took to be the product layer.

My question really has to do with that layer. I moved it using a dropper to a petri dish to let it evaporate but come next day it just seemed to stain the walls of the container around it yellow. I had it in a plastic bag just in case it tipped while in my drawer. Far as I can tell, it wasn't disturbed but it did manage to turn everything inside yellow. Unfortunately, I'm guessing that's the iodine? There was still plenty of the purple fluid in the dish which I then transferred to a dropper bottle. I have left the bottle open in hopes the fluid will evaporate as it still smells like lighter fluid. Do I have any reason to keep the purple solution? If so why?
If it does evaporate, would I be left with pure iodine? If so, what happened to the potassium iodide? Again folks please forgive the simplicity of these questions. This literally is my first foray into chemistry. I'm very excited but I want to understand as much as possible every step of the way.

Anyhow, I'll leave it at that for the time being. I really am so grateful for this forum and all of you. thank you in advance for your attention to my questions.

P.S. a bit off topic I'm sure, but I understand I have to seek out permissions for certain chat rooms or forums? is this still true. Anyone in particular I need to speak to?
Cheers. thanks all and good night


[Edited on 6-3-2014 by Sigerson]

[Edited on 6-3-2014 by Sigerson]

Sigerson - 5-3-2014 at 20:44

Also, what would keep me from just adding more Lighter Fluid and extracting more out of the solution. I did it with two t. Tubes and they definitely looked lighter when I was done with em but sill dark enough to indicate more iodine to extract?

thesmug - 5-3-2014 at 21:50

I have that book too! The yellow staining is from iodine, which tends to stain everything yellow. I don't think there's much use in keeping the purple solution but yes, if you evaporate it I believe you will be left with pure iodine. The iodine will, however, sublime quickly and because of this you might lose a lot of iodine, so be sure to pay attention to any purple vapor. If I'm understanding your question correctly the potassium iodide was (assuming you're using HCl to produce said iodine) converted into potassium chloride, iodine and water, or hydroiodic acid and potassium chloride if you didn't add the H2O2. The eq. for this reaction is: 2HCl + 2KI + H2O2 ---> I2 + 2KCl + 2H2O. I believe the permission-only forums require at least 100 good posts (not being a jerk, not spamming etc...). Adding more lighter fluid wouldn't do much other than make a dilute solution if you have already extracted all the water/KCl solution. I hope you have a good time doing all the experiments in that book!

[Edited on 3/6/14 by thesmug]

Mesa - 6-3-2014 at 02:37

What is reducing the KI to I2? Or are you only trying to extract the 1.27% of free iodine and leaving the KI in the aqueous layer? I'm not familiar with the experiment myself, nor with the chemistry of Iodine salts in general, however it is interesting to me that I2 will migrate to an organic solvent from an aqueous one so readily.

In any case, Iodine stains skin with a fairly obvious yellow tint, perhaps a similar reaction is occuring with something coating the walls of the petri dish?

Metacelsus - 6-3-2014 at 10:50

The KI is most definitely left in the solution.

@Mesa: Iodine is more soluble in organic solvents than water (log Pow = 2.49)

The yellow color is due to staining from the iodine vapor.

Sigerson - 6-3-2014 at 20:37

Thanks for the replies all of you. Ill give a synopsis of the experiment. According to Bob Thompson's illustrated guide, lab 6:4, solvent extraction, I filled one test tube half way with tap water. I then added 10ml of iodine solution. It says to use Lugols solution but I used an iodine solution I assumed to be the same. It has 1.27 Iodine, and about 1.67 KI (potassium Iodide). I mixed this solution vigorously. I did this again in a second test tube. so now with two test tubes mixed with iodine solution and water, in one of them I added 1ml of lighter fluid as my organic solvent, allowing it to form a layer at the top of the aqueous solution. I repeated the process in the second test tube, this time using 5ml of lighter fluid. I mixed both and eventually, a purple layer form at the top which I understand to be the product layer. I extracted the product layer and added it to a petri dish and stored it in a plastic drawer. you're right, it eventually evaporate and turned everything yellow. Is that to say there's no iodine left after everything evaporates? I put the remainder of the purple solution in a dropper bottle. Should I toss it then?

thesmug - 6-3-2014 at 20:47

Quote: Originally posted by Sigerson  
Thanks for the replies all of you. Ill give a synopsis of the experiment. According to Bob Thompson's illustrated guide, lab 6:4, solvent extraction, I filled one test tube half way with tap water. I then added 10ml of iodine solution. It says to use Lugols solution but I used an iodine solution I assumed to be the same. It has 1.27 Iodine, and about 1.67 KI (potassium Iodide). I mixed this solution vigorously. I did this again in a second test tube. so now with two test tubes mixed with iodine solution and water, in one of them I added 1ml of lighter fluid as my organic solvent, allowing it to form a layer at the top of the aqueous solution. I repeated the process in the second test tube, this time using 5ml of lighter fluid. I mixed both and eventually, a purple layer form at the top which I understand to be the product layer. I extracted the product layer and added it to a petri dish and stored it in a plastic drawer. you're right, it eventually evaporate and turned everything yellow. Is that to say there's no iodine left after everything evaporates? I put the remainder of the purple solution in a dropper bottle. Should I toss it then?

What you have is iodine water. If you wan't you can throw it away but I believe you can still use it for any application which would require iodine in solution.